Carriage traversing mechanism



'Feb. 2, 1937. w. H. HOWE 9,

CARRIAGE TRAVERSING MECHANISM Filed lay 1s,'-1es3 2 Sheets-Sheet 1 g? I Carfl'qya Favorso E Z v j 0 6/ g 10/ 2;

E 109 7 I Z 4:! WMW A 1 4223 1 1 Feb. 2, 1937. w. H. HOWE 7 2,069,493

CARRiAGE TRAVERSING MECHANISM Filed May 16, 1933 2 sheets-sheet 2 Q 6W, xii? 32, 44% W UNITED STATES PATENT OFFICE CARRIAGE TRAVERSING MECHANISM Application May 16, 1933, Serial No. 671,362

9Claims. ((31.172-240) This invention relates to electric mechanism for producing traversing motions of a traversing carriage, such, for example, as the work table of a universal grinder or similar machines, al-

though it should be understood that it is not limited to any particular type of mechanism. It is more particularly suitable .for light, slow speed service which involves certain special difliculties. Heretoiore it has usually been found necessary to employ some type of load and fire mechanism in such service in order to insure reversal of the traversing motor after its motion in one direction has been stopped, as by the con tact of the carriage with a switch opening dog,

there being too little over-travel of the carriage after the motor switch has been opened to in sure closing of the motor connections for reverse carriage travel.

In accordance with the present invention no load and fire mechanism is necessary, closing of a switch at one end of the carriage traverse and opening the switch at the other end of its travel serving to open and reverse the motor connections. An automatic time delay mechanism for cutting down the energy supplied to the motor for a predetermined time after reversal isemployed to prevent unduly heavy motor stopping and starting current and to control the motion of the carriage to effect a dwell at the traverse limits and to control its deceleration and acceleration adjacent thereto.

Means may also be provided according to this invention for increasing the motor field strength at the lower speeds of carriage travel, which improves the speed regulation under varying loads.

For a more complete understanding of this invention, reference may be had tothe accompanying drawings, of which,

Figure 1 is a diagram of a feed motor control mechanism embodying this invention.

Figure 2 is a front elevation of a grinding machine to which the mechanism may be applied.

Figure 3 is a detail section through the housing for the traversing motor.

Figure 4 is a detail section transverse to the section of Figure 3 and showing part of the driving connection from the traversing motor to the table.

Figure 5 is a detail section to a larger scale on line 5-5 of Figure 2. I

Figure 6 is a detail section on line 66 of Figure 5.

Referring to Figure 1 of the drawings, at I is shown a universal reversible motor which may be connected by any suitable means to drive a reciprocating carriage or table as is well known in the art. At 2 is shown a single-pole singlethrow switch, which is preferably of the mercury type, so arranged as to close a circuit when tipped in one direction and to open the circuit 5 when tipped in the opposite direction. As shown this switch is provided with an actuating arm 3 which may be struck at suitable times by dogs 4 and 5 on the traversing carriage, thereby to tip the switch alternately in opposite directions to 1 open and close the circuit controlled thereby at opposite limits of motion of the traversing carriage in a manner well known in the art. This switch 2 controls a circuit, deriving its energy as from an auto-transformer indicated generally 15 at 6. in which circuit is interposed the energizing coil 1 of a double-pole double-throw relay 8 so that when the switch 2 is closed, as in the position shown in the drawings, this relay is energized to close contacts at a and b and c and d, respec- 2O tively. Current passes from the transformer tap I00 through the line IOI to the switch 2, thence through the lead I02, through the coil I and through the lead I03 to the transformer tap I04. In the connections as shown, the in-put leads 20 25 and 2| also connect directly to the leads I03 and MI, respectively, but the lead 2| may be connected to other transformer taps IOIla, I00b or I000 to thereby vary the voltage impressed on the motor. When the switch 2 is in open posi- 30 tion this relay 8 is de-energized and the contacts a, b and c, d are opened and the contacts e, f and g, h are closed. The contacts a, b and e, f control the connections to the reverse motor field windings I0 and Il of the motor i, thus to con- 35 trol the direction of rotation of this motor, so that when the switch 2 is closed the motor is energized to move the carriage in a direction to bring the dog 4 toward the arm 3, which at the end of this traverse will act to move the arm 3 40 to the right to an extent suflicient to open the switch 2, whereupon the field coil I0 01 the motor is de-energized and the field coil Ii becomes energized so that the motor reverses and the carriage is moved in the opposite direction. The 45 field coils l0 and II have the common lead I05, which also is connected to one side of the motor armature M. Means are provided for preventing an undue rush of current when each reversal takes place and to control the deceleration and :50 acceleration of the motor and produce a dwell at the end of the stroke as will iater be described. The motor 6 as shown in this figure derives its energy from the auto-transformer 6 through a selective transformer tap switch indicated gen 55 I erally at or e, I, through the lead I01 to the lead I03 and the transformer tap I04. As shown this switch I5 is in position to make connection with the transformer tap it, the taps k and l of the transformer being of relatively low voltage, while the taps m and n are higher voltage taps. When either of the lower voltage taps k and l are connected some or all of the resistance I6 is inserted in parallel with the armature circuit of the motor I through the lead I05. This lowers the effective resistance of the armature circuit and thus tends to increase the total current flow, but since the total current passes through the field winding, this in effect increases the field current at the lower speeds, which tends to increase the fieldstrength and improves the speed regulation under varying load, and also somewhat increases the acceleration of the motor after each reversal. smaller is the value of the resistance thus inserted to correspondingly increase the field strength.

In order to prevent excessive current flow to the motor I at each reversal and to provide desirable speed control of the carriage, provision is made for automatically decreasing the energy supplied to the motor for a definite predetermined time after each reversal. This as-shown is done by introducing a resistor 25 in the motor circuit I, this resistance being arranged to be short circuited after a predetermined time after each reversal of the connections to the motor I. The short circuiting mechanism is connected at opposite ends at either end of the resistance 25 at the points a: and 1 through the leads I08 and the leads I03 and I09. It includes therein in parallel normally closed relay-actuated switches 26 and 21 between the leads I08 and I09 which switches are arranged to be opened on energization of their respective relay coils 28 and 29. These relay coils 28 and 29 are arranged in series with each other and also in series with a pair of inductances 30 and 3|, and the circuit including the two inductances 30 and 3|, and both the relay coils 28 and 29, isfed direct current from any suitable source as by means of the rectifying tube 33 receiving energy from the transformer 6. This tube as shown is of the two-plate type, one plate being connected to one end of the main winding of the auto-transformer 6 through lead H and the other being connected to the alternating current power supply line 2I through the lead IOI. The filament of this tube is energizedv through the coil 34 of the auto-transformer and direct filament-plate current smoothed out by the filter system comprising the condensers 35,

the choke 35, and the resistance 31 is fed through lead III to one side of the circuit comprising the inductances 30 and 3i and the relay coils 28 and 29, the return being back through lead I09 to the mid-point of the auto-transformer through the point 3 Either one or the other of the relay coils 28 or 29, together with its co'inpan'ion inductance 30 or 3|, is arranged to be short circuited so as to form a closed circuit path including both, on reversal of the motor whereupon the inductance in the short circuited portion continues to force current through the companion The lower the voltage, the

relay coil 20 or 29 for a certain length of time before this current dies out. When this current dies out the relay will release its switch and short circuit the resistance 25 therethrough. The short circuiting of these delay circuits, each of which includes an inductance and its connection relay 28 or 29, is produced by closing the contacts at c, d or g, h of the relay 8. Closing contacts 0, (1 connect the line II2 leading from one side of the relay 28 to the lead III through the inductance 30 and lead Ill to the opposite side of the relay 28. Similarly closing of contacts g, h connects lead II2 from one side of the relay 29 to lead I09 through inductance 3I and lead II to the opposite end of the relay 29.

Thus when the carriage has reached that end of its traverse where the switch 2 is thrown to energize the relay coils I, contact is made between c and d. This acts to short circuit the delay system comprising the inductance 30 and the relay coil 28 and when the current in this short circuiteddelay system fails to a certain extent the switch 26 springs closed, thus short circuiting the resistance 25 and interposing the full voltage as determined by the setting of the switch I5 on the carriage actuating motor. When the carriage reaches its other limit of motion and tripsthe switch 2 to de-energize the relay coil I, the contacts a, b are opened and the contacts e, f are closed, thus reversing the motor connections and at the same time the contacts 0, d are opened and the contacts 9, h are closed. The opening of the contacts 0, d opens the short circuit of the resistance 25 through the switch 26 and the closing of the contacts g, it short circuits the delay system including the inductance 3I and the relay coil 29 and after the current in this short circuited delay system dies down sufficiently the switch 21 closes and short circuits the resistance 25. Inreach position of the relay 8, the rectifier tube continues to feed direct current through the inductance and the delay action relay coil which are not short circuited. The length of time that the resistance 25 remains actively interposed in the motor circuit may be adjusted independently at each end of the carriage traverse by the setting of the variable resistances 43 and 44 which are connected across the inductances 30 and 3I. It will be noted that this delay mechanism is controlled by electrically responsive means so that it requires only very simple elements. Not only does this resistance 25 act to prevent an undue rush of current at the instant the motor connections are reversed, but it also effects a dwell at the ends of the carriage stroke and produces a gradual deceleration and then a gradual acceleration before and after the dwell, these rates, as well as the length of the dwell, being adjustable independently at opposite ends of the carriage stroke by varying the resistances 43 and 44.

Figures 2 to 6, inclusive, show the application of this invention to a grinding machine. Referring to these figures at 50 is shown the carriage of a grinding machine supported for axial travel on the bed 5|. This carriage is shown as supporting a head stock 52 at one end and a tail stock 53 at the opposite end, these stocks being adjustable from and toward each other to suit the length of the work, as is well understood. The head stock is shown as provided with a live center 54 and the tail stock with a dead center 55 between which work to be ground is placed. At 56 is shown a stationary stand forrotatably supporting a grinding wheel 51 past which the is connected through a train of gearing indicatedgenerally at 62 to the'motor l to be driven there- 'In Figures 3 and 4 this motor I is shown as mounted in a suitable frame housing 55 and on the end of its armature shaft 66 to which is secured a gear 61 forming a part of the gear train 62 is secured a metallic disk 10 for rotation in its plane by rotation of the shaft 68. Preferably this disk is of copper or aluminum and it is rigidly attached to the armature shaft 66 was to rotate therewith. Thisdisk extends between the poles ll of an electromagnet l2 and this electromagnet is energized by direct current, which, as shown in Figure 1, may be obtained from the rectifier system including the rectifier tube 33 and which is shown as employed to energize the delay relay coils 28 and 29 and the inductances 30 and 3|. The coil 13 of the elcctremagnet 12 may be connected as shown in Figure 1 to the lead I03, a variable resistance 14 being employed in series therewith and connecting to the lead H3 extending to the filament of the tube 33 so as to control the amount of current flow through the coil 13. Electric current flow in the disk induced by rotation of the disk between the poles of magnet produces a reactive force tending to oppose the rotation of the disk. This opposing force is proportional to the speed of rotation of the motor within quite wide limits of speed of rotation. It thus acts as a brake tending to cause the motor to operate at a constant speed. Since the torque of the motor varies inversely with its speed while the retarding torque of this brake varies directly with the speed, at a certain speed the driving and retarding forces will be equal leaving no energy for acceleration or deceleration of the motor. Further, the acceleration-of the motor immediately after it starts will be more rapid than were a frictional brake employed, since at lower speeds the retarding torque is materially reduced over that at full speed. The use of this brake instead of relying on frictional loss and output power as limits to motor speed has several advantages. The motor has a lower maximum speed and is thus more quiet and has less wear. Frictional losses are variable, particularly in case a considerable part of the friction is in an oil immersed gear train, in which resistance varies with temperature, while the disk brake is not subject to the effects of these variables. Furthermore, by supplying the motor and the brake from the same electrical powersource, both driving and retarding torque will vary directly with voltage, this resulting in negligible speed variations of the motor from this cause. Further, there is no mechanical contact between moving parts involved with this disk brake so that there is nothing to wear or deteriorate.

It should be understood, however, that the carriage traversing mechanism may operate without using such a brake if this is desired. it being no way essential to the effectiveness of the reverse mechanism per sc.

Figures 5 and 6 illustrate a mounting for the mercury switch 2, as shown it being carried by a rock shaft 80 which carries on its inner end a lever 8| provided with contact elements 82 at opposite ends.

held in an inward position by means of a spring with this invention for several reasons.

This rock shaft 80 is normally 83 surrounding a reduced portion 84 thereof and seated in a socket 85 in-the carriage 58. In this inward position the contact elements 82 are in position to impinge upon the inclined faces 81 of the dogs 4 and 5 at either end of the stroke of the table, thus to cause making'or breaking of the circuit through the switch 2 as has been previously described. To the outer end of the rock shaft 80 is secured a handle 50 which may be grasped and the rock shaft pulled outwardly against the pressure of the spring 85, soas to bring the elements 82 out of operative position,

and a screw 9| may then be tightened to hold the shaft 80 in this inoperative position. This screw Ell may also be adjusted to impart a controlled,

frictional resistance to the rocking of the shaft 80. The handle 90 also makes possible hand actuation of the switch 2 without reference to the dogs 4 and 5 in case at any time it should be desired to reverse the direction of motion of the table intermediate its normal limits of reciprocation.

It will be notedthat the usual load and fire mechanism is unnecessary in a machine provided versal of the direction of motion is controlled by the making and breaking of a single contact and there is'no effect whatever until this contact has either been made or broken to reverse the direction of driving. Even the merest trace of over travel, which always occurs in measurable amount. serves to ensure the hold of the mercury and point contact in either make or break position. Moreover, a mercury switch as ordinarily made has inherently a tendency to stay in the position of make or break inwhich it'is positioned at any time as. due to liquid friction and surface adhesion, the mercury does not flow until the switch tube has perceptibly passed the center point. Likewise also the tubes are com monly made with a slight curvature which acts to prevent return flow until the switch tube has passed the control point in the opposite direction. There is also sufficient friction-in the rock mechanism so that there is no tendency to rock the switch except as this accompanied by the action of the dogs 4 and 5 or by the manual rocking of the handle 96.

From the foregoing description of an embodiment of this invention it should be evident to end of the carriage traverse, means for automatically reducing the supply of energy to said motor at each reversal for a predetermined period, and means for independently adjusting the length of said period at opposite ends of the carriage traverse.

2. A traversing carriage actuatinginechanism comprising a. reversible electric carriage-driving motor, a. relay normally connecting said motor for one direction of motion and when energized establishing reverse direction motor connections, a switch in operative relation to said carriageto be closed at one end of said carriage traverse and The reopened at the other end of said carriage traverse for controlling the energization of said relay, and means for operatively inter-posing and maintaining for a predetermined time a resistance in the establishing reverse direction motor Connections,

motor circuit at each reversal of motor connections.

3. A traversing carriage actuating mechanism comprising a reversible electric carriage-driving motor, a relay normally connecting said motor for one direction ofmotion and when energized a switch in operative relation to said carriage to be closed at one end of said carriage traverse and opened at the other end of said carriage traverse for controlling the energization of said relay, a resistance in the motor circuit, and means acting a predetermined time after each reversal of said motor connections for short circuiting said re sistance. 1 I

4. A traversing carriage actuating mechanism comprising a reversible electric carriage-driving motor, a relay normally connecting said motor tion, an inductance in series with said connection relay, a source of direct current for energizing said connection relay, and means actuated at the end of a carriage traverse for short circuiting said connection relay and inductance.

' 5. A traversing carriage actuating mechanism comprising a reversible electric carriage driving motor, a relay normally connecting said motor i'or-one direction of motion andwhen energized establishing reverse direction motor connections,

a switch in operative relation to said carriage to for controlling the 'energization of said relay, a

be closed at one end of said carriage traverse and i opened at the other end of said carriage traverse resistance in the motor circuit, a pair of connections each normally short circuiting said resistance, a relay for each connection when energized interrupting its connection, an inductance in series with each connection relay, and a source of direct current for energizing said connection relays, said motor relay when energized short circuiting one of saidconnecting relays and its inductance and when de-energized short circuiting the other of said connection relays and it inductance.

6. A traversing carriage actuating mechanism L comprising a reversible'electric carriage driving motor, a relay normally connecting said motor for one direction of motion and when energized establishing reverse direction motor connections, a switch in operative relation to said carriage to be closed at one end of said carriage traverse and opened at the other end of said carriage traverse for controlling the energization of said relay, a resistance in the motor circuit, a pair of connections each normally short circuiting said resist ance, a relay for each connection when energized interrupting said connection, an inductance in series with each connection relay,a source of direct current for energizing said connection relays, said motor relay when energized short circomprising a reversible electric carriage-driving motor,. a relay normally connecting said motor for one direction of motion and when energized establishing reversed motion connections, a rockable mercury switch carried by said carriage and controlling theenergization of said relay, stationary dogs and cooperating elements on said carriage for effecting rocking of, said switch to' open or close connections to said relay at opposite ends of traverse of said carriage, a rock shaft for carrying said switch, means for yieldingly holding said rock shaft in axial position with said elements operatively related to said dogs, and means actuable to move said shaft axially from said position against the pressure of said yieldingly holding means.

8..A traversing carriage actuating mechanism comprising .a series motor, a source of energy for driving said motor, connections driven by said motor for traversing said carriage, a metallic disk connected for rotation in its plane by said motor, an electromagnet havingspaced poles between which said disk extends, and a direct current supply for energizing said electromagnet.

9. A traversing carriage actuating mechanism comprising a series motor, a source of energy for driving said motor; connections driven by said motor for traversing saidcarriage, a metallic disk connected for rotation in its plane by said motor, an electromagnet having spaced portions between which said disk extends, and a direct current supply derived from said source for energizing said electromagnet.-

WILFRED H. HOWE. 

